These days, many people spend all their time away from their job working on their side hustle. When you spend the weekend grinding, Monday morning hurts that much worse.
Get serious about taking a day off regularly. Turn off your phone. Do boring stuff like puzzles or go mini-golfing with your spouse. Visit your parents.
No, this won't cripple your side hustle. Ever try to remember a name, and the more effort you put into it, the harder it is to remember? Business breakthroughs can be like that, too.